The present invention relates to safety protection for XDSL, all digital subscriber loops circuitry and, more particularly, to a safety protection system and the related system operational method for the electrical protection of users of XDSL circuitry, which is based on continuous monitoring of the current or voltage parameters on one or both of the exchange and the remote subscriber ends of the XDSL communication system.
Very often the required operational electrical power of the remote subscriber unit must be directly fed from the communication system exchange side. Good examples for such a remote power supply are pair gain systems. There are various safety standards such as EN60950 and DIN57-0800 part 3e, which generally do not allow for the system end units drive voltage to exceed 120 volts for DC voltage supply and 50 volts R.M.S. for the case of AC voltage supply. Currents over 60 MA on telephone wires are not permitted by the relevant safety standards.
When it is required to supply the operational driving power to the remote subscriber unit from the exchange unit, through the XDSL communication system, there is a power limit on the maximum available drive power. The power limit is the product of the relevant safety standards' maximum allowed current with the maximum allowed voltage.
Present art XDSL communication systems subscriber unit operational power requirements do not meet the relevant safety standards power limitation demands, with voltages as high as 320 volts DC prevalent. However the current limit of 60 MA is generally strictly observed.
Several safety hazardous situations might be occurred which involve the misuse of XDSL communication systems. In particular a hazardous situation might develop when a person touches one or both of the wires of the XDSL communication system. If only one wire is touched, the person in touch creates through his body a low impedance electrical path to ground, through this single wire. If the XDSL system is designed to be fully electrically floating, then no current will pass through the person touching the wire, as the entire system will then float to ground. If the XDSL communication system will not be fully floating the hazardous safety situation of a person touching only one of the system's wires will cause an unbalanced load when measured from the exchange output leads, where one wire shows a low impedance path to ground while the other wire shows the remote unit load. Another hazardous situation might develop when a person touches both system wires, in this case some of the system current will flow through the low impedance electrical path presented by the touching person body, instead of driving the remote unit load.
It is required to prevent currents that are higher than the safety limit of 25 MA to flow through the person touching the system wires. Other maximum allowable current level safety limits might be defined and secured by the safety system, but it is believed that the threshold limit on currents not to exceed 25 MA is required, as higher currents are believed to be harmful to the human body.
There is a recognized need for, and it would be highly advantageous to have a safety system and a related safety protection method that would enable enhanced XDSL communication system safety.